Chapter 30

Arthropods

Section 1: Features of Arthropods

Section 2: Spiders and Other Arachnids

Section 3: Insects and Their Relatives

Section 4: Crustaceans

Section 1

Features of Arthropods

Objectives:•Summarize the evolutionary relationship of arthropods and annelids.•Identify three subphyla of arthropods.•Describe the characteristics of arthropods.•Describe how growth occurs in arthropods.

Section 1

Features of Arthropods

Jointed Appendages•Jointed Appendages All arthropods have jointed appendages that are modified to perform different functions.

Section 1

Features of Arthropods

Arthropod Diversity•Classification Arthropods are grouped into three subphyla: Chelicerata, Uniramia, and Crustacea.

Section 1

Features of Arthropods

Arthropod Body Plan•Segmentation All arthropods have three distinct regions—the head, the thorax, and the abdomen.•Compound Eyes Most arthropods have compound eye, which are made up of thousands of individual visual units.•Exoskeleton Arthropods have an exoskeleton made of chitin.•Molting Molting is a process when arthropods discard the exoskeleton.

Section 1

Features of Arthropods

Arthropod Body Plan continued•Respiration Air enters the arthropod’s body through spiracles and passes into the tracheae, delivering oxygen throughout the body.•Excretion Arthropods have a unique excretory system called Malpighian tubules that efficiently conserves water and eliminates metabolic wastes.

Section 2

Spiders and Other Arachnids

Objectives:•Summarize the characteristics of arachnids.•Identify the internal and external characteristics of brown recluse spiders.•Compare spiders, ticks, and mites.•Identify the health threats posed by some arachnids.

Section 2

Spiders and Other Arachnids

Arachnid Modifications•Chelicerata Members of subphylum Chelicerata have mouthparts, called chelicerae, that are modified into fangs or pincers.•Spiders Spiders have a head and a cephalothorax, no antennae, six or eight pairs of simple eyes, a pair of fangs and pedipalps, and four pairs of walking legs.

Section 2

Spiders and Other Arachnids

Scorpions and Mites•Scorpions Scorpions have pedipalps modified into large, grasping pincers. A stinger is located at the end of their abdomen.•Mites Mites have body parts that are fused to form an unsegmented body. Many mites transmit diseases.

Section 3

Insects and Their Relatives

Objectives:•Describe the characteristics of insects.•Compare complete and incomplete metamorphosis.•Identify the external and internal structures of the Eastern Lubber grasshopper.•Compare millipedes and centipedes with insects.

Section 3

Insects and Their Relatives

Insect Diversity•Species of Insects Insects make up more than half of all named animal species.•Insect Body Plan All insects have a body plan with three body sections (head, thorax, and abdomen), three pairs of legs (all attached to the thorax), and one pair of antennae.•Insect Life Cycle The life cycles of insects are complex and involve a process of change called metamorphosis, during which larvae change into the adult insects.

Section 3

Insects and Their Relatives

Insect Diversity continued•Flight Insects were the first animals to have wings.•Social Insects Hymenoptera and Isoptera have elaborate social systems.•Insect Relatives Centipedes and millipedes are related to insects, but they have numerous segments.

Section 4

Crustaceans

Objectives:•Summarize how crustaceans and insects are similar and dissimilar.•Describe the body plan of decapods.

Section 4

Crustaceans

Crustacean Habitats•Characteristics Most crustaceans have branched appendages, two pairs of antennae, three chewing appendages, walking legs attached to the thorax, and gills. Like insects, crustaceans have jaws called mandibles. Crustaceans have a distinctive larval form called a nauplius and crustaceans live in the world’s oceans.

Section 4

Crustaceans

Terrestrial Crustaceans•Common Examples The most widespread terrestrial crustaceans are pill bugs and sow bugs.

Section 4

Crustaceans

Aquatic Crustaceans•Copapods and Krill Copepods and krill, which are tiny marine crustaceans, are the chief food of many marine species.•Decapods Large marine crustaceans such as shrimps, lobsters, and crabs, have five pairs of legs.•Sessile Crustaceans Barnacles are sessile as adults.